It is only recently that astronomers have learned that supermassive black holes are also found in dwarf galaxies. Before scientists had time to get used to this fact, the universe presented a new surprise. It turned out that many "heavyweights" are by no means at the center of their star systems.
The discovery is described in a scientific article published in the Astrophysical Journal by a group led by Amy Reines of the University of Montana.
In the centers of large galaxies with hundreds of billions of stars, supermassive black holes are usually lurking. (Recall that a black hole is called supermassive if its mass is at least a million solar.) But what about dwarf galaxies, in which there are only a few billion stars?
Until recently, it was believed that such animals were not found in them. But in 2011, Reines and co-authors published an article about the discovery of the first supermassive black hole at the center of a dwarf star system.
Astronomers have launched a systematic search for dwarf galaxies with supermassive black holes, finding about a hundred such systems.
"As soon as I started specifically looking for these objects, I found a whole bunch," - says Reines.
Amy Rines has made her second discovery that is reversing the idea of dwarf galaxies.
Photo by Adrian Sanchez-Gonzalez / MSU.
Part of this work was the new research. The authors selected 111 galaxies within a billion light years. In each system, the total mass of stars did not exceed three billion suns. Astronomers observed these objects using the VLA radio telescope system. Black holes were identified by the radiation of matter falling on them.
The authors selected 13 systems that almost certainly contain a supermassive black hole. And then the scientists were in for a surprise: in most of these galaxies, the "monster" did not live in the center.
"All the black holes I discovered earlier were in the centers of galaxies. These same ones roamed the outskirts. I was amazed when I saw this," Raines admits.
Note that in the past year, another group of astronomers published interesting results of computer simulations. Experts then came out that with a probability of 50%, a supermassive black hole in a dwarf galaxy would be located not in the center, but thousands of light years away. Now observations have confirmed this bold conclusion.
"Escape from the center" may be the result of the gravitational effects of neighboring star systems, scientists suggest. In addition, a black hole may not be "native" for a given galaxy, but inherited from a collision with a neighbor. (It is also possible that the black hole just got tired of traffic jams and dirty air in the center and moved to a quieter area).
In connection with the current results, experts propose to change the approach to the search for supermassive black holes in small stellar systems.
"We need to expand the search area to cover the entire galaxy, and not just its core, where, as we previously expected, there could only be a black hole," says Reins.